Biosonar adjustments to target range of echolocating bottlenose dolphins (Tursiops sp.) in the wild

F. H. Jensen, L. Bejder, M. Wahlberg, P. T. Madsen

Research output: Contribution to journalArticlepeer-review

71 Scopus citations

Abstract

Toothed whales use echolocation to locate and track prey. Most knowledge of toothed whale echolocation stems from studies on trained animals, and little is known about how toothed whales regulate and use their biosonar systems in the wild. Recent research suggests that an automatic gain control mechanism in delphinid biosonars adjusts the biosonar output to the one-way transmission loss to the target, possibly a consequence of pneumatic restrictions in how fast the sound generator can be actuated and still maintain high outputs. This study examines the relationships between target range (R), click intervals, and source levels of wild bottlenose dolphins (Tursiops sp.) by recording regular (non-buzz) echolocation clicks with a linear hydrophone array. Dolphins clicked faster with decreasing distance to the array, reflecting a decreasing delay between the outgoing echolocation click and the returning array echo. However, for interclick intervals longer than 30-40ms, source levels were not limited by the repetition rate. Thus, pneumatic constraints in the sound-production apparatus cannot account for source level adjustments to range as a possible automatic gain control mechanism for target ranges longer than a few body lengths of the dolphin. Source level estimates drop with reducing range between the echolocating dolphins and the target as a function of 17 log(R). This may indicate either (1) an active form of time-varying gain in the biosonar independent of click intervals or (2) a bias in array recordings towards a 20log(R) relationship for apparent source levels introduced by a threshold on received click levels included in the analysis.

Original languageEnglish (US)
Pages (from-to)1078-1086
Number of pages9
JournalJournal of Experimental Biology
Volume212
Issue number8
DOIs
StatePublished - Apr 15 2009
Externally publishedYes

Keywords

  • Automatic gain control
  • Biosonar
  • Dolphin
  • Echolocation
  • Sound production
  • Tursiops

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Physiology
  • Aquatic Science
  • Animal Science and Zoology
  • Molecular Biology
  • Insect Science

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